Aerospace manufacturers increasingly use composite materials to reduce the weight and increase the performance of some components, thereby reducing the weight and improving the efficiency of aircraft.
Composite materials used by the aerospace industry typically comprise a fibrous material in a polymer matrix. A composite component comprising a fibrous material in a matrix material may be produced by arranging one or more ply layers of fibrous material on a mould tool and curing the component to form a consolidated component. Typically, the fibrous material is provided in the form of one or more “pre-preg” layers. Alternatively one or more “dry” ply layers may be arranged on a mould tool and a matrix material may be applied to the ply layers. Typically the component is cooked or “cured” at elevated temperature and pressure in an autoclave. Alternatively, some matrix materials may not require the increased pressure provided by an autoclave so that the component may be cured at elevated temperature in an oven.
Curing a composite component in an autoclave or oven is a time consuming process, typically lasting for approximately four hours. The cycle time is limited by the time taken for the autoclave or oven, the component and the tooling to reach the desired curing temperature. The curing process also uses a large amount of energy because the autoclave or oven itself is heated as well as the component.
Microwaves may be used to cure a composite component in order to reduce the time of the curing process. One known method of microwave curing is described in US2010/0163480. A microwave-sensitive material in contact with a composite part is heated by microwaves. The composite part is heated partly by absorbing microwaves, and partly by being in contact with the heated microwave-sensitive material. Another known method of microwave curing is described in JP2006107 (A). A composite panel is fixed into a frame. The composite panel and the frame are formed from the same material. The frame is heated by microwaves and this heat is transmitted to the panel.
However, a problem with known microwave curing methods, including those described in US2010/016348 and JP2006107 (A), is that non-uniform absorption of microwaves by the composite component may lead to a non-uniform temperature distribution through the component as it cures, with “hot spots” and “cold spots” present. These “hot spots” and “cold spots” may be difficult to predict, monitor and control, and may result in reduced and unpredictable performance of the component.
It is, therefore, desirable to provide a method for curing a composite component using microwaves which reduces or controls the unpredictable nature of the temperature distribution in the component.